Combination oscillator coil and erasing head for magnetic recorders



June 13, 1944.

M. CAMRAS COMBINATION OSCILLATOR COIL AND ERASING HEAD FOR MAGNETIC RECORDERS 'Filed Nov. 18, 1942 7 1 uv UU I), i G /2 m0 26 k 4o 4 33 31 F 32 30 z f c /4 22 3 /3 I 2 I0 =r' f Znrzsanlczr Patented June 13, 1944 UNITED STATES PATENT OFFICE COMBINATION OSCILLATOR COIL AND , ERASING HEAD FDR NIAGNETIO RECORD- ERS Marvin Camras, Chicago, 111., assignor to Armour Research Foundation, Chicago, 111., a corporation of Illinois Application November 18, 1942, Serial No. 465,968

Claims. (01. 179-10(i.2)

. amagnetic tape or wire, it is desirable to provide,

means for demagnetizing the recording medium magnetlzing arrangement or erasing head, it is possible to place a new recording upon a wire or other medium already having a recording thereon, without the necessity of first demagnitizing the medium in a separate operation before run-' ning it through the recording device.

Magnetic recording devices may be made in the form of a compact instrumentality for easy transportation. Such an instrument, of course, embodies complicated electrical circuits includ ing oscillatory, amplifying and various other types of circuits, and in most instances the electrical apparatus and wiring is crowded into a relatively small space. The crowded condition is increased in the event the instrument is of the type that both makes a recording and also reproduces a made recording since a speaker and fur ther circuit arrangement are then added. It is further desirable, therefore, to keep the instrument as compact as possible in-size and yet not sacrifice any useful equipment or arrangement in the electrical circuits.

With the foregoing in mind, it is an important object of the instant invention to provide a circuit and apparatus arrangement for a magnetic recording device wherein an instrumentality embodied in and forming a part of an electrical circuit is caused to perform an additional function extraneous to the particular circuit in which it is included, and thus eliminate the necessity of providing additional means to perform that tional function.

Another object of the invention resides in the provision of a circuit and apparatus arrangement for a magnetic recording device wherein an in ductance coil is included in the recording circuit, and this inductance coil is given a position other than that which it would usually'occupy, so that the inductance coil performs an additional function extraneous to the function it performs in the particularcircuit in which it is included.

Stillanother feature of the invention resides addiin the provision of a magnetic recording arrangement including an oscillatory circuit, and wherein the oscillating coil from that circuit is made to perform an additional and extra function outside of its normal function in the oscillatory circuit.

still another feature of this invention resides in the provision of a magnetic recorder arrangement in which the magnetizing circuit includes an oscillating coil, which coil is positioned so that the recording medium will be affected by the coil before reaching the recording head of the apparatus. and so be demagnetized prior to being magnetized by the recording head of the apparatus.

'A. further object of the invention resides in the provision of a magnetic recorder arrangement-wherein a high frequency oscillating coil forms a component part of the recording circuit, and wherein the same oscillating coil functions as an erasing head to demagnetize the recording medium prior to the actual making of the recording on that medium. a r

It is also an object of the invention to provide a magnetic recorder arrangement including-an electrical circuit, with a. component part of that electrical circuit performing the extra dutyof functioning as an erasing head in connection with the paramagnetic medium upon which a recording is made.

While some of the more salient features, char-" acteristics and advantages of the instant inven tion have been above pointed out, others will become' apparent from the following disclosures; taken in conjunction with the accompanying drawing, in which:

The single figure is a simplified diagrammaticillustration showing certain salient parts of the apparatus embodied in the magnetic recorder;-

together with a simplified electrical circuit, including means embodying P inciples of the instant' invention.

As shown on the drawing:-

In the illustrated embodiment of this invention there is shown a verysimplified circuit and apparatus arrangement for a magnetic recorder. Many parts of the magnetic recorder and vari-- ous other circuits which may be included in the magnetic recorder'are'omitted, since the inven-' tion centers itself in the recording circuit and immediately associated apparatusparticularly.

In the upper portion of the figure there is shown a magnetic recording head generally indicated by numeral i which is in the form of} an electromagnet. The head includes a core 2, preferably-laminated, which in its upper leg divid- .An elongated paramagnetic recording medium I, which in the illustrated instance is shown in the form of a very fine round wire. travels over or through the top portion of the magnetizing head I during the making. of a recording. Sections of this medium are successively magnetized as they pass over the slot 3 in the recording head in accordance with the variations of the sound being recorded. In many cases, it is desired to place another recording upon, a wire which is already magnetized in accordance with a previous recording, It is not. deemed desirable to take the wire and rewind it in some other location for purposes of demagnetizing the wire, which would result in two separate winding operations. With I the apparatus; illustrated. it is possible to record upon an. already magnetized wire without the previous recording aifecting the one being made in any degree. With this arrangement, the wire 1 passes through or adjacent a demagnetizing or erasing head, illustrated in the form of a'coil 8, on its ,way to the. magnetizing head I, so that when the. wire actually. reaches the magnetizin head. it is.c l ean" or thoroughly demagnetized. Thus, if arecording. medium is already carrying a recording for which there is no further use, that same recording medium, normally wound upon. a reel or spool, may be inserted in the instant machine, and operated Just as though the mediumwere entirely demagnetized, because the medium actually will be demagnetized by the erasing headB before it reaches the recording head I.

In a magnetic recording device, the recording head, together with oppositely disposed reels or spools upon which the recording medium is wound for travel in either direction, and associated apparatus such as guide pulleys and level winding elements are usually mounted upon a panel in a readily accessible position. The electrical ap paratus and wiring therefore are usually disposed in compact association within a cabinet, and frequently if the particular recorder is made so that it will also reproduce a recording, the interior of the cabinet is in a rather crowded condition, since it is desirable to have the entire apparatus in as compact a form as possible. The crowded condition within the cabinet or casing would be further materially aggravated in the event a separate demagnetizing circuit was provided; i. e., an erasing head and circuit connections therefor in addition to the other electrical apparatus and wiring necessary to perform the recording and reproducing operations. The present invention seeks to simplify as much as possible the apparatus within the recorder casing and therefore rely upon an instrumentality which is a component part of one of the essential electrical circuits, repositions this instrumentality so that the recording medium I will pass through it on the way to the recorder head I, and causes it to perform the additional function of demagnetizing the recording medium. This' instru-- mentality, in order to acquire the dual result, is preferably disposed on the aforesaid panel in a readily accessible position, and thus to acquire the benefit oi the dual function, it is only necessary to mount the particular instrumentality in a location foreign to that which it would normally occupy if it were only to perform its particular .function in the circuit in which it is embodied.

' head I, and thus be demagnetized by the coil.

The oscillating coil 8 is therefore made to function as an erasing head for the magnetic recording device, and it accomplishes this additional result while performing its necessary function as a component part of the oscillatory circuit.

The simplified circuit arrangement selected for illustration includes an oscillator tube 9 in the form of a triode which has its cathode I0 connected through a conductor to a ground I2. The plate I3 of the tube 9 is connected through conductor I4 to one end of the aforesaid inductance coil 8, and an intermediate tap is taken on this coil-by way of a. conductor I5 which returns to a positive line wire I6. A negative line wire I1 is connected through conductor I8 to the aforesaid conductor II. The two line wires I6 and I1 maybe associated with any suitable source of direct current, and a by-pass condenser It is preferably connected across the line wires.

The opposite end of the inductance coil 8 is connected to a conductor 20 which'leads to one end of the aforesaid coil '6 in the magnetizing head I, and the opposite end of the coil 6 is connected through a conductor 2I to the aforesaid conductor Ill. The conductor 20, of course, carrice the output of the oscillatory circuit which includes the inductance coil 8 and a tuned circuit condenser 22 connected across the conductors I4 and 20 in parallel with the inductance coil 8.

The feed-back through the grid 23 of the tube 8 is through a conductor 24 connected at one end to the grid and at the other end to timescillating circuit output conductor 20. The -alternating component of the plate current passing through the inductance coil 8 will set up an (iscillating current of high frequency in the os'cillating circuit, and a grid blocking condenser 25 is included .in the conductor 24 to keep the high voltage off the grid of the tube. A grid biasing resistance'26 is connected across the grid by a conductor 2'! which joins the conductor 24 on the grid side of the blocking condenser 25 and connects with the ground conductor II from the cathode I 0 of the tube.

As mentioned above, the lower or audio frequency circuit is superimposed upon the high frequency output of'the oscillating circuit. This audio circuit includes a. microphone 28 or equivalent sound pickup device connected at one side by a conductor 29 through a suitable amplifying arrangement, diagrammatically indicated at30. to the aforesaid conductor '2l from the magnetizing coil 6. The other side of the pickup 28 is connected by way of conductor 3| to the aforesaid amplifier 30 and an output conductor 3Ia connects to conductor 20 leading from the other end of the magnetizing coil 6. In this conductor 3Ia a choke coil or the equivalent 32 is included which blocks out high frequency from the microphone circuit and passes low frequency. To prevent low frequency current from the audio circuit reaching the oscillating circuit, a blocking convariations in the magnetic field set up in the magnetizing head I in accordance with variations of'sound being recorded on the medium 1.

The inductance or oscillatin coil 8 would normally occupy a position within the casing of the apparatus much more closely t-the condenser 22. However, by moving this inductance coil 8 to a position so that the recording medium 1 will have to pass through or by theinductance coil wise than necessitated by the scope of the appended claims.

I claim as my invention: 1. In a magnetic recording arrangement wherein a sound recording is made by magnetizing an elongated medium, a magnetizin head including a coil for magnetizing the medium, an

oscillator arranged to feed said coil, said'oscillator having a frequency determining circuit including an inductance coil, and said inductance coil being positioned so the medium must pass through the thus vary the'high frequency current and cause magnetic field produced therebyand be demagnetized before reaching said magnetizing head.

2. In a magnetic recording arrangement wherein a recording of fluctuatin'g electrical energy is made by magnetizing an elongated medium, means for magnetizing the medium, an alternating current electrical circuit for energizing said means, a frequency determining coil in on its way to the magnetizing head so as to travel through the magnetic field of the coil, the inductance coil also performs the extra and added function of'an erasing head,;that is. ,it. damag netizes' the medium prior to the medium reach-" ing the recording head i. Regardless of whether or notthe recording medium is already mag netized in accordance with a previous recordin said circuit and forming a part thereof, and said 1 coil being positioned to acton said medium and demagnetize the same before the medium is acted on by said means.

3. In a magnetic recording arrangement, a recording head to record by magnetizing a traveling elongated recording medium, an electrical circuit to energize said recording head including an oscillator, and a. combination frequency determining coil and erasing head in said circuit through the magnetic field of which the medium travels on its way to said recording head.

the high frequency alternating current -in..the"

coil 8 will demagnetize or clean the wire prior to-its reaching the recording head I. Thus, the

disposition of .the coil 8 not only eliminates the need for a complete demagnetizing circuit either in conjunction with the recording device or such a demagnetizing arrangement at some other location but eliminates the need for demagnetizing a wire inan entirely separate operation before the-wire is used in the recording device. Not only are extra connections and the material therefor 4. In a magnetic recorder of the type wherein a traveling recording medium is successively magnetized in accordance with variations in electrical impulses, a high frequenc oscillator-"circuit having a frequency determining coil therein, 'said frequency determining coil being disposed in'such -a position that the record medium passes in close eliminated by virtue of the disposition of the coil 8, but the compactness of the entire recording device is enhanced, and there is not only a resultant saving of material but also a resultant saving in the cost of operation of the device since no more energy is used in the oscillating circuit above described than would be used it the demagnetizing operation were eliminated.

It will, of course. be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon other proximity thereto, whereby said coil performs the dual function of erasing any previous magnetization on said record medium and also determines the frequency of oscillation of said oscillator circu t.

5. A magnetic recorder comprising a magnetizing coil, an erasing coil, said coils being arranged to have a traveling record medium pass through the magnetic fields produced thereby, and a source of high frequency oscillations arranged to supply high frequency electric energy to said magnetizing coil, at least a portion of said erasing coil also being a frequency determining element of said source or high frequency oscillations.

MARVIN CAMRAS. 

